The present invention may be advantageously used for producing high-velocity jets of low-viscosity liquids. Use of such jets for cutting and dimensional machining of materials, cutting and demolishing of rocks and structural members, cleaning various types of metal production and chemical equipment offers a number of advantages as compared with conventional production processes, such as an improvement of labor productivity and safety, savings of materials, pollution reduction and the like.
The most preferable field of the invention is cleaning of castings from high-strength moulding sand, such as the removal of core sand from the inner cavities of turbine blades to be cooled during operation, the cavities having a substantial extent with small cross-sections and intiricate configuration.
Producing high-velocity jets of low-viscosity liquids requires elevated pressure levels. It should be, however, noted that an increase of working pressure level was hampered by a movable contact seal which was prone to a rapid wear during operation due to high contact pressure which was proportional to the working pressure. In addition, high contact pressure in the friction pair piston/contact seal resulted in a considerable increase of friction forces whose work was completely converted into heat thus resulting in considerable heating of component parts thereby leading to scoring and jamming of movable parts and to destruction of the contact seal. The attempts to prolong the service life of pumps brought about the development of contactless seals.
Employment of contactless seals for conventional low-viscosity working fluids having the viscosity which is substantially unchanged with pressure increase (for example, water) resulted in considerable energy losses due to a leakage of a certain part of liquid through a slit space thus impairing the pump efficiency. The energy associated with leakage was released in the form of heat in the slit seal zone and resulted in heating, scoring and jamming of movable parts of the pump.
The above-mentioned disadvantages have been eliminated by using, in high-pressure pumps, two different liquids rather than one: one liquid is a working liquid having physical properties which are required for a predetermined production process, and the other liquid is a sealing liquid having a high viscosity which is considerably increased with pressure growth.
This high-pressure pump using liquids of different viscosity comprises a housing accommodating a movable piston defining a space communicating with a working liquid source and with a user via non-return valves. There is provided another space between the piston and the housing which communicates with a source of a sealing liquid via radial passages of the housing. This space communicates, via a slit seal comprising an annular space between the piston and the housing, on one side with the working liquid space and on the other side, via another slit seal comprising an annular space between the piston and the housing, with atmosphere.
The source of a sealing liquid is under pressure which is greater than the delivery pressure of the pump.
In the course of reciprocations of the piston in the housing, the working liquid flows through the intake and delivery non-return valves and is fed to a consumer under a desired pressure.
The sealing liquid is fed from the source under a pressure which is greater than the working liquid pressure and is constantly admitted, via a radial passage of the housing, to the sealing liquid space and discharged, via the slit seals, into the atmosphere and into the working liquid space thus insulating the working liquid from atmosphere and providing lubrication of the parts in frictional engagement.
The main disadvantages of the above-described pump are as follows:
the use of an auxiliary source of a sealing liquid under a pressure which is greater than the working pressure of the pump which results, among other things, in additional energy losses;
penetration of considerable amount of sealing liquid into the working liquid which requires either use of liquids having similar properties or provision of an auxiliary device for separating the sealing liquid from the working liquid;
discharge of the sealing liquid into atmosphere and feeding it back into the sealing liquid space which is associated with additional energy losses;
insufficient cooling of parts in frictional engagement since the piston moves in the zone of two slit seals. This fact is especially important for high-speed pumps;
considerable size of the pump, especially the length due to the provision of two slit seals.
Another conventional construction of a high-pressure pump partially eliminates the above disadvantages.
Said construction comprises a housing accommodating a movable piston defining a chamber, a partition member movable coaxially with the piston which divides the chamber into two spaces substantially insulated from each other. One space communicates with a source of working liquid and with a consumer via non-return valves, and the other space communicates, on one side, with a low-pressure sealing liquid source via a non-return valve, and on the other side, with the atmosphere via a slit seal comprising an annular space formed between the piston and the pump housing. The housing of the pump is provided with a stop for limiting the displacement of the partition member during the intake stroke which is mounted within the sealing liquid space.
Low-pressure sources of sealing and working liquid comprise low-pressure pumps supplied from tanks.
During the reciprocations of the piston in the housing, the working liquid flows through non-return intake and delivery valves and is fed to a consumer under a desired pressure.
Pressure from the pump piston is transmitted to the working liquid through the sealing liquid and partition member.
During the delivery stroke of the pump, the non-return intake valve is closed and the non-return delivery valve is open for feeding the working liquid to a consumer under a desired pressure.
During this stroke, the non-return valve connecting the sealing liquid space to the low-pressure pump is closed. The partition member moves coaxially with the piston in the same direction therewith, but at a lower speed which is determined by a predetermined discharge of the sealing liquid into atmosphere through the slit seal. As a result, the partition member is brought closer to the pump piston during the delivery stroke.
During the intake stroke, the non-return delivery valve is closed, and the intake valve is open. The working liquid is fed from the pump operating under a pressure above the pressure of the sealing liquid pump, to the working space for displacing the partition member in the same direction with the piston. The displacement of the partition member during the intake stroke is limited by a stop which is rigidly connected with the housing and mounted within the sealing liquid space. After the partition member is stopped by the stop, the piston continues its movement, the non-return valve connecting the sealing liquid space to the pump is open, and this space is refilled with a certain volume of sealing liquid to compensate for its leakage through the slit seal during the intake stroke. Then the cycle is repeated.
The main disadvantages of this construction are as follows:
absence of cooling of parts in frictional engagement since the piston is insulated by the partition member from the working liquid which has better parameters and physical properties as regards heat exchange than the sealing liquid;
discharge of sealing liquid into atmosphere resulting in additional energy losses for pumping it back into the sealing liquid space;
excessive length of the low-pressure pump for working liquid as compared to the length of the pump for sealing liquid, because the partition member is returned back into the initial position during the intake stroke under the pressure of the working liquid to bear against the stop mounted within the sealing liquid space. This also results in additional energy losses.